1. Field of the Invention
The invention relates to the field of providing a method of producing networks of crystalline low melting metal oxides comprised of one-dimensional nanostructures such as nanotubes and nanowires in an arrangement of wires forming crystalline networks defined as “nanowebs”, “nanowire networks”, and/or “two-dimensional nanowires” containing wire densities on the order of 109/cm2.
2. Description of the Prior Art
Nanostructures find unique applications in electronics, optoelectronics, and catalysis due to their high surface to volume ratio, enhanced material characteristics due to quantum confinement effects and the high fraction of chemically similar surface sites. Functionalization of these nanostructures can only be achieved and become useful through the synthesis of bulk quantities of defined structures with controlled composition, crystallinity and morphology. Gallium oxide, for example, is a wide-bandgap material and is of interest due to its interesting bulk properties such as conduction and luminescence. These properties make it a candidate for gas sensing, catalytic, and optoelectronic device applications. Nanostructures of gallium oxide will be of particular interest for these applications.
Gallium oxide (Ga2O3) is a wide-bandgap semiconductor with a band gap of 4.9 eV at room temperature. In the form of nanowires, Ga2O3 emits blue light, and when activated with manganese, can act as an electroluminescent phosphor. Polycrystalline Ga2O3 thin films are excellent sensors for oxygen (at temperatures, T>850° C.) and reducing gases (T<900° C.). One-dimensional (1-D) nanostructures of Ga2O3 have traditionally been produced by arc discharge, laser ablation, chemical vapor deposition, chemical transport reactions, and thermal evaporation. Nano-wires, -rods, -belts and -ribbons, are among the diverse one dimensional structures. Their growth has been attributed to either the catalytically assisted vapor-liquid-solid (VLS) process, the vapor-solid (VS) process, or a combination of the two.
More particularly, gallium oxide nanowires have been synthesized using techniques such as physical evaporation, arc discharge, and catalyst assisted methods. All of these techniques have been thought to proceed according to two primary mechanisms. The first mechanism involves carbothermal reduction of gallium oxide to produce gas phase gallium suboxide growth species. The second mechanism relies on transition metal catalyst or evaporated gallium clusters to provide the necessary template for size control of the resulting nanowires.
Although nanoscale metal oxide networks have been fabricated previously, the current techniques produce porous, amorphous, web-like structures. Up until now, only advanced tools such as electron beam lithography were able to assemble nanostructures, by selectively transferring nano-building blocks, or by surfactant induced mesoscopic organization, and redox templating synthesis of inorganic metal wires. However, these tools are still too slow and cost-prohibitive for the assembly of large-area networks of nanomaterials for device fabrication.
The present invention provides a process for rapid self-assembly of low melting metals and/or their oxides, such as gallium oxide (Ga2O3) nanowires into a network. These are not precise nano-structures, but unlike fractal networks, the Ga2O3 nanowires will be shown to intersect and form webs parallel to the substrate. The two-dimensional, polygonal arrangement of wires is unique. The growth mechanism of these low melting metal oxides to form gallium oxide nanowebs is provided as an example and is extendible to other low melting metals and their oxides such as for example: zinc oxide, tin oxide, aluminum oxide, bismuth oxide, and titanium dioxide.